Actually, the whites displaced the Iroquois, who displaced the Ojibway, who displaced the Sioux from the northern lake country onto the plains. Then the Sioux got the horse and learned to fight.
My point was just like other people around the world, the American Indians had tribes who were warlike and conquered other tribes, and peaceful tribes who just wanted to be left alone. In short, American Indians were like everybody else of the planet.... a mix of good and bad.